There are many types of interlock switches available on the market today that are utilized in many applications such as circuit card assemblies. These switches utilize a variety of basic switch configurations which typically require additional components to achieve a maintenance position and a wide range of actuation displacement to accommodate application tolerances.
Interlock switches used in circuit card applications must be capable of operating in three distinct positions known in the art as the maintenance position, the normal position, and the actuation zone or position.
When the switch is set in the maintenance position, it must be capable of remaining in this position until it is manually moved into one of the two other positions.
A switch that is set in the actuation zone or position must be capable of returning to the normal position from the actuation zone or position described below, when actuation forces are removed from the switch. The switch must also pass through the normal position when traveling from the maintenance position to the actuation zone or position.
When the switch is set in the actuation zone the switch must be capable of automatically returning to the normal position when the switch is released. Thus, the actuation zone is basically a momentary position. Further, this position is described as a "zone" because a wide range of actuation displacement is required in order to accommodate application tolerances.
Prior art interlock switches are plagued with a number of shortcomings when implemented on a circuit card assembly. For example, prior art interlock switches consume a significant amount of area on the circuit card assembly. This area can typically be on the order of approximately 1.09 square inches.
Typical prior art interlock switches have other shortcomings as well. Prior art interlock switches are relatively expensive to produce in high volume where they typically cost approximately $10.00 a piece. Moreover, these devices use a slider action where the frictional forces result from normal (perpendicular) forces generated by the basic switch. These frictional forces can create problems if the sliding surface finishes as well as the assembly geometry are not carefully controlled. Hence, the design reliability of such devices is manufacturing process sensitive. Further, since prior art interlock switches must be soldered to the circuit card assembly, they must go through post solder cleaning. This exposes the basic switch contacts to contamination from cleaning solvents unless the switch happens to be a sealed unit. In certain contact arrangements, the contacts are susceptible to intermittence after exposure to such contaminants. Still further, the soldering operation including the necessary mounting hardware for installing the prior art switches to circuit card assemblies is costly. The total part count in prior art switches can typically be 25 to 30 parts. Finally, the circuit configurations controlled by prior art interlock switches are limited by the electrical function of the basic switch. Many of these switches are double pole single throw switches where only one circuit can be completed for each pole.
It is, therefore, an object of the present invention to provide an improved interlock switch that eliminates the aforementioned shortcomings of the prior art interlock switches.